Expanded polystyrene is usually produced in blocks having the shape of a parallelepiped and is supplied in that form to users, who use cutting operations to obtain slabs or other three-dimensional shapes from it, necessary for their specific requirements.
Such blocks are fully formed, in a single operation, in moulds, fully perforated, into which a suitable quantity of loose polystyrene spheres is poured, which is then struck, substantially on all sides, by a flow of steam that penetrates from the walls of the mould in which there are openings, causing the mass to expand. In this way the polystyrene spheres are made to expand and stick to one another, forming a single body having the shape of a block or parallelepiped.
In the specific use of the material for producing panels, in particular for building, slabs are obtained from the above-mentioned blocks, by making a corresponding cut, slabs which, obviously, in terms of the longitudinal dimension (usually corresponding to the height of the panel when fitted) have the same length as the block produced in that way.
With reference to this, the blocks, and the relative moulds, have a limited range of standardised dimensions, in particular of lengths available, substantially corresponding to the most common height dimensions of the panel slabs produced.
When, as it is often the case, the height of the panels does not correspond precisely to the length of a standardised block, a corresponding portion of the block must be cut, consequently producing material waste, and as a result waste or problems and costs for disposal.